Is my shematics good ?

Discussion in 'The Projects Forum' started by retrobotic, Oct 9, 2013.

  1. retrobotic

    Thread Starter New Member

    Oct 9, 2013
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    Hi there ! :D

    I've to drive a truck wiper motor ( 24V 180W ). To do that, i've creat a circuit based on two SPDT relays http://www.ebay.fr/itm/SLA-24VDC-SL-C-24V-DC-SONGLE-Power-Relay-PCB-Type-/140817295747?pt=LH_DefaultDomain_0&hash=item20c95d6983 drived by two NPN transistor ( TIP20 ).


    PS : The pads on te schematics ares outputs for motors or for switchs

    PS² : Normally i have a ACS715 chip on my shematics but i'ts not there because i cannot find it in libraries.

    Thanks :)

    And sorry for my english :/
     
  2. Experimentonomen

    Member

    Feb 16, 2011
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    -this thread is gonna get closed, to find out why read the rules.
     
  3. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Not necessarily. Retrobotic, what are you doing with the motor?
     
  4. Experimentonomen

    Member

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    Its quite clear its a windshield wiper interval timer project with the inputs setting the different interval times.
     
  5. DerStrom8

    Well-Known Member

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    Oops, I misread the first sentence. I thought the OP said he/she HAS a windshield wiper motor, instead of has TO drive a windshield wiper motor.

    You're right, this thread will probably be closed. We'll see what the moderators think though.

    Regards,
    Matt
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    There could be a HAS/TO misinterpretation due to non English speaker?
    Maybe a confirmation first before premature censorship?
    Max.
     
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  7. DerStrom8

    Well-Known Member

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    Good point, Max.
     
  8. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Retrobotic - What is the motor for?

    Just so the OP clearly knows that we've asked for this information.
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Note his title: "Is my shematics good?"

    I believe he's building a robot.

    A female robot.
     
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  10. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It's not that clear to me. Why couldn't it be a control for the "head" of a robot, that turned right or left based on different input signals to the PIC?
     
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  11. retrobotic

    Thread Starter New Member

    Oct 9, 2013
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    The schematics is in fact a prototype for a trash compactor. The motor is as I said a truck wiper motor. The motor turns a screw that moves the piston who crushe wastes.

    So i have to control the motor direction forward and backward but not control it speed.

    The ATTiny84 control transistors ( TIP120 ) who control relays.

    I'm effectively not english but french :/
     
  12. DerStrom8

    Well-Known Member

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    That sounds fine, I don't think this thread will need to be closed after all.

    Last I knew, google translate did very well translating from french to english. I suggest you try that--you can type what you want to say in your native language and it will convert it to English for you. It's worth a try :)

    Regards,
    Matt
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It looks to me as though you should have the N.C. contact connected to Common (GND) of the motor supply on both relays, this will also give you regenerative braking as well as normally off.
    IOW when you want the motor idle. both output are OFF, picking up either relay will rotate each direction.
    You can also use a FET to drive the relay, such as a TTL to up to 60vdc 2N7000, you can also remove the base resistor.
    The way you show the schematic, the motor will always rotate with outputs off.
    Max.
     
    Last edited: Oct 10, 2013
  14. Experimentonomen

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    Feb 16, 2011
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    Wat?!:confused: Shorting the motor is dissipative breaking. To achieve regen breaking you need a boost converter to drive a current back into the source to bring the voltage up.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You are thinking of Dynamic braking.
    Regenerative braking is a system in which the electric motor acts as a generator where the energy can be recycled or can be injected into a resistive load if the energy is high to dissipate the regenerative voltage, and in turn the resultant current causes an effective braking effect.
    Max.
     
  16. Experimentonomen

    Member

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    And in order to recycle that energy you need to use a boost converter and raise the voltage a few volts above that of the source in order to create a charging current back into the source. The number of volts above source determines the charging current as well as how much of a braking effect the motor will encounter.

    If the "generator" and source voltages are the same, no charging current will occur
     
  17. MaxHeadRoom

    Expert

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    There is no source voltage, it is removed.
    Do a simple test, if you have a P.M. motor of any kind, Just short the terminal wires and try and spin the motor as fast as possible!
    The regenerative energy current will be evident.
    You will get the picture.
    Max.
     
  18. retrobotic

    Thread Starter New Member

    Oct 9, 2013
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    Something like that ?

    Did i have to put freewheel diode on my relay ?

    I've heard that i have to put my 4700µF capacitor between 24V and 0V. Is 0V = GND ?
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes, correct and you should put a reverse diode across the coil.
    Also on my discussion about braking, transpose the terms I used, Dynamic for regenerative and vice-versa, (due to a mental aberration), sorry :rolleyes:
    And also it is usual to have mechanical interlock, but on a SPST relay it is not possible, so make sure you do it in software, i.e. turn off #1 relay before powering the opposite one #2 and vice-versa.
    Max.
     
  20. retrobotic

    Thread Starter New Member

    Oct 9, 2013
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